Transmission protocols used to transmit serial data between connected devices are constantly in the process of being revised with new and improved versions being deployed every few years. Examples of such protocols include the DisplayPort standard, the High-Definition Multimedia Interface (HDMI) standard, the Serial ATA standard, the Peripheral Component Interconnect Express (PCI-E) standard, and the Universal Serial Bus (USB) standard. While the continued evolution of these and other protocols is generally desirable, it is important to provide support for legacy devices during the remainder of their useful lives.